how to understand the permissible voltage and current of film capacitor?

Question

I use the 0.12uF metallized polyester film capacitor Model ECQE2124JB which has 250VDC rated voltage. I have a sine wave across the capacitor, then can I think that the maximum AC voltage is 250/1.414=176.8 Vrms? But from the characteristic datasheet, the permissible voltage is less than 40Vrms at sinewave. What's the difference? If I use the capacitor in a LC resonant circuit, does it mean the RMS resonant voltage cannot exceed 40Vrms?
In my opinion, the permissible current is calculated as I = 2*pifC*V, for my application f = 10KHz, so I = 2*3.14*10kHz*0.12uF*250V=1.884Ap = 1.33Arms. Is it right? But from the characteristic datasheet, the permissible current is only about 0.2Arms. Why that?
In my LC resonant application, the mearsured current across the capacitor reaches 3.5Arms, but the peak voltage will not exceed 250VDC. It also conflicts with Vrms = Irms *Xc, where Xc is the impedance of the capacitor.

https://industrial.panasonic.com/ww/products/capacitors/film-capacitors/film-cap-electroequip/ecqeb-dc-rated/ECQE2124JB

Answer 1

Excess voltage will cause the capacitor to fail due to dielectric breakdown.

Excess current will cause the capacitor to fail due to overheating (because of the equivalent series resistance of the capacitor). Since an AC voltage implies an AC current as the capacitor charges and discharges, an AC voltage can lead to overheating failure at a lower voltage than the DC voltage that would cause dielectric breakdown.

So you have two different failure mechanisms, and you need to consider different limitations to avoid these two types of failure.